Specimen stage for an electron microscope

ABSTRACT

A specimen stage for an electron microscope which allows tilting and translation of the specimen. The translation does not shift the tilt axes. Thus, once the point of intersection of the tilt axes is aligned with the optical axis, it will remain aligned irrespective of subsequent translation of the specimen. Thus, tilting of the specimen will not affect the field of view. The stage comprises first and second gimbals, the second gimbal carrying a specimen mounting. The second gimbal can be translated with respect to the first gimbal along the second gimbal axis. The specimen mounting can be translated with respect to the second gimbal in a direction inclined to the second gimbal axis. In a preferred embodiment, the first gimbal is a tube, and the second gimbal is an annulus supported within the tube.

United States Patent Lucas Nov. 7, 1972 [54] SPECIMEN STAGE FOR AN [211 App]. No.: 168,615

[30] Foreign Application Priority Data Aug. 4, 1970 Great Britain ..37,64ll70 [52] US. Cl ..250/49.5 B, 250/65 R [51] Int. Cl ..H0lj 37/20 [58] Field of Search ..250/49.5 B, 65 R [56] References Cited UNITED STATES PATENTS Valore ..250/49.5 B

Primary Examiner-James W. Lawrence Assistant Examiner-C. E. Church Att0mey-Watts, Hoffmann, Fisher & l-leinke [5 7 ABSTRACT A specimen stage for an electron microscope which allows tilting and translation of the specimen. The translation does not shift the tilt axes. Thus, once the point of intersection of the tilt axes is aligned with the optical axis, it will remain aligned irrespective of subsequent translation of the specimen. Thus, tilting of the specimen will not affect the field of view. The stage comprises first and second gimbals, the second gimbal carrying a specimen mounting. The second gimbal can be translated with respect to the first gimbal along the second gimbal axis. The specimen mounting can be translated with respect to the second gimbal in a direction inclined to the second gimbal axis. In a preferred embodiment, the first gimbal is a tube, and the second gimbal is an annulus supported within the tube.

9 Claims, 4 Drawing Figures SPECIMEN STAGE FOR AN ELECTRON MICROSCOPE BACKGROUND OF THE INVENTION This invention relates to specimen stages for electron microscopes.

In electron microscopy it is often required to perform certain positioning operations on a specimen while the specimen is under observation. Thus, it is often required to tilt the specimen about two mutually inclined axes with respect to the electron optical axis of the microscope. This allows the specimen to be viewed from a range of different angles. Additionally, it may be required to translate the specimen in two mutually inclined directions in a plane transverse to the electron optical axis. This allows different portions of the specimen to be brought into alignment with the optical axis and therefore into the field of view of the microscope.

Where tilting of the specimen is provided, it is desirable that the specimen stage be so arranged that the tilt axes intersect the optical axis. If the specimen is tilted about an axis which does not intersect the optical axis, the region of the specimen under observation will move laterally with respect to the optical axis. This region will therefore tend to move out of the field of view of the microscope. The field of view can be restored by applying a translational movement to the specimen simultaneously with the tilting. However, this must usually be done in a stepwise manner, and the procedure is therefore very slow and tedious, and results in the specimen being exposed to long doses of radiation.

In most known stages which provide both translational movement and tilting of the specimen, applying translational movement to the specimen also shifts the tilt axes relative to the optical axis. Thus, in such a stage, it is impossible to maintain alignment of the tilt axes and the optical axis while observing different regions of the specimen.

SUMMARY OF THE INVENTION The invention overcomes this difficulty by providing a specimen stage in which translational movement can be applied to the specimen without affecting the position of the tilt axes. Then, if the point of intersection of the tilt axes is initially aligned with the optical axis, it will remain aligned irrespective of the translational movement applied to the specimen.

The specimen stage comprises a support, a first gimbal pivotally mounted on the support for rotation about a first axis, and a second gimbal pivotally mounted on the first gimbal for rotation about a second axis which is inclined to and intersects the first axis. A specimen mounting is carried by the second gimbal. Thus, by tilting the gimbals about their axes, a specimen in the specimen mounting can be tilted about two mutually inclined axes with respect to the optical axis of the microscope. Means are provided for translating the second gimbal relative to the first gimbal in a direction parallel to the second gimbal axis. This permits translation of the specimen in that direction without affecting the positions of the gimbal axes. Means are also provided for translating the specimen mounting relative to the second gimbal in a direction inclined to the second gimbal axis. This permits translation of the specimen in that direction also, without affecting the positions of the gimbal axes.

It is to be understood that the term gimbal as used herein is not intended to be restricted to a ring-shaped member. The gimbals may be of any convenient shape. In a particular embodiment, for example, the first gimbal is a tubular member.

Accordingly, it is the principal object of the invention to provide a specimen stage for an electron microscope for tilting and translating a specimen, wherein the specimen can be translated without affecting the positions of the tilt axes.

BRIEF DESCRIPTION OF THE DRAWINGS This and other objects and advantages of the invention will become apparent from the following description of a preferred embodiment of the invention, as read in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic sectional elevation of an electron microscope;

FIG. 2 is a diagrammatic sectional plan view of the specimen stage of the microscope as seen from the plane indicated by the line 2--2 in FIG. 1;

FIG. 3 is an enlarged diagrammatic sectional plan view of a portion of the specimen stage of FIG. 2; and

FIG. 4 is a cut-away perspective view of a portion of the specimen cartridge shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the electron microscope comprises a generally tubular evacuable housing 10 at one end of which is mounted an electron gun 12 for producing a beam of electrons directed along the axis 14 of the housing 10. The axis 14 constitutes the optical axis of the microscope, and is referred to as the Z axis.

The electrons pass through a pair of condenser lenses l6, 18 which focus the beam to a fine spot. A specimen stage 20 is provided for supporting a specimen at this spot.

Electrons transmitted through the specimen pass through an objective lens 22 and a pair of projector lenses 24, 26, which produce a magnified electron optical image of a portion of the specimen. This image is made visible by means of a fluorescent screen 28 positioned in a viewing chamber 30 which is provided with an observation window 52.

Referring to FIG. 2, the specimen stage 20 includes first and second support blocks 38, 40. The first block 38 is slidably mounted on a plane surface 42 within the microscope housing 10, the surface 42 being perpendicular to the optical axis 14. The block 38 is guided by rollers 44 for linear movement, the direction of this movement being referred to as the x-axis. This movement is controlled by a screw-threaded rod 46 which bears against the block 38. The second block 40 is slidably mounted on the plane surface 42, within the first block 38, and is guided by rollers 48 for linear movement in a direction (referred to as the Y-axis) perpendicular to the X-axis. This movement is controlled by a screw-threaded rod 49 which bears against the block 40. Return springs (not shown) are provided for maintaining the blocks 38, 40 in contact with the respective threaded rods 46, 49.

The block 40 has an aperture 41 aligned with the optical axis 14, in order to permit the passage of the electron beam.

The inner block 40 has a raised portion 50 with a cylindrical aperture 52 which is adapted to receive a tubular specimen cartridge 54. The cartridge 54 is inserted into the microscope via an airlock (not shown) in the wall of the housing 10, and is located by engagement of an enlarged external diameter portion 55 of the cartridge 54 with the internal surface of the aperture 52. The cartridge 54 extends in the direction of the Y- axis, and can be rotated about its axis of symmetry by means of gears (not shown) meshing with a ring gear on the portion 55. This rotation is referred to as the Y-tilt.

Referring to FIGS. 3 and 4, these show the tubular specimen cartridge 54 in greater detail. An annular member 56 is pivotally supported within the tubular cartridge 54 by means of journals 58, 60 which are supported in bearing recesses 62 in the cartridge 54. In this way, the annular member 56 is pivotal about an axis perpendicular to the Y-axis. This pivoting is referred to as the X tilt, since it is about the x-axis when the Y-tilt is zero. The annular member 56 carries a specimen mounting 64 which is adapted to receive a specimen 66.

Thus, the tubular cartridge 54 and the annular member 56 constitute gimbals for tilting the specimen 66 about two mutually perpendicular, intersecting axes with respect to the electron optical axis 14.

The cartridge 54 has a pair of diametrically opposite slots 65, 67 which permit an electron bema travelling along the axis 14 to pass through the specimen 66. These slots 65, 67 are elongated in the circumferential direction in order to allow for rotation of the cartridge 54 about the Y-axis.

The X tilt is produced by means of an operating rod 70, slidably mounted in the tubular cartridge 54 and carrying a rack 72 which engages with a pinion 74 on the journal 58. The rod 70 engages a push rod 76 which slides within a raised portion 78 of the inner block 40. The push rod 76 has an enlarged end portion 77, so as to allow for rotation of the cartridge 54.

The journals 58, 60 can slide axially in their bearings so as to allow a translational movement of the annular member 56 in the direction of the X tilt axis. This movement is referred to as the X movement. When the annular member 56 is moved in this way, the pinion 74 slides under the rack 72 so as to accommodate the movement. The X movement is imparted to the annular member 56 by means of a bell-crank lever 76 pivotally mounted within the tubular cartridge 54. One end of the lever 76 carries a ball 78 which fits in an annular groove 80 in the journal 58. The other end of the lever 76 is activated by an operating rod 82, housed in the tubular cartridge 54.

The operating rod 82 is connected, via slot 81 in the cartridge 54, to an operating ring 83 which slides on the outside of the tubular cartridge 54.

The specimen mounting 64 is movable linearly within the annular member 56 in a direction perpendicular to the X tilt axis, this movement being referred to as the Y movement.

The Y movement is imparted to the specimen mounting 64 by means of a mechanical coupling comprising a bell-crank lever 84 a push rod 86, and a further bell-crank lever 88. The push rod 86 passes axially through the journal 60, and bears at its inner end upon one end of the bell-crank lever 88 which converts the longitudinal motion of the push rod 86 in the X direction into movement of the mounting 64 in the Y direction. The mounting 64 is tensioned against the bell-crank lever 88 by means of a spring 90 while the bell-crank lever 88 is tensioned against the push rod 86 by means of a spring 92. The push rod 86 is provided with a return spring 94,mounted within the journal 60. Movement of the push rod 86 is produced by the bellcrank lever 84, which is pivotally mounted in a housing 96, pivotally attached to the journal 60, so as to allow the annular member 56 to be rotated without the housing 96 rotating. One end of the bell-crank lever 84 carries a ball 98 which fits in an annular groove 100 in the outer end of the push rod 86, while the other end of the lever 84 carries a ball 102 which fits slidably in a slot 104 in an operating rod 106, slideably mounted within the tubular cartridge 54. The operating rod 106 is connected via slot in the cartridge 54, to an operating ring 107 which slides on the outside of the cartridge 54.

It will be seen that movement of the operating ring 107 produces translational movement of the specimen mounting 64 in Y direction, by way of the coupling 106, 84, 86, 88. It will also be seen that, when the annular member 56 is moved in the X direction, the ball 102 slides within its slot 104 to accommodate this X movement, so that no movement of the bell-crank lever 84 is produced, and hence no Y movement of the specimen mounting 64. Thus, the Y movement of the mounting 64 is independent of the X movement of the annular member 56.

Movement of the two operating rings 83, 107 is effected by means of respective fork levers 108, 110. These fork levers 108, 110 are mounted on pivots 112 on the block 40, and are coupled to external controls (not shown). Compression springs 114, 116 are provided to maintain contact between the operating rings 83, 107 and their respective fork levers 108, 110.

The gap between the prongs of the fork lever 110 is larger than the external diameter of the operating ring 107, so as to allow the cartridge 54 to be withdrawn from the specimen stage without interfering with the fork lever 110.

In operation, a specimen 66 is mounted on the specimen mounting 64. The tubular member 54 is then inserted into the specimen stage, via the airlock (not shown). The support 40 is then adjusted by means of rods 46, 49 to bring the point of intersection of X and Y goniometer tilt axes into alignment with the optical axis Z. Tilt can then be applied, as required, to the specimen 66 by tilting the tubular member 54 and the annular member 56, it being possible to tilt the specimen in any required direction in this manner, up to a certain maximum amount of tilt. Since the tilt axes are centred on the optical axis, there will be no lateral movement of the observed point of the specimen when the X and Y tilts are applied, and hence no change in the field of view.

The specimen can be translated, to search for features of interest, by applying the X and Y translational movements to the specimen mounting 64 by means of the rings 83, 107 operating control rods 82 and 106. These movements do not shift the X and Y tilt axes. Therefore, these axes remain aligned with the Z axis throughout the examination of the specimen.

It will be appreciated that the invention may be applied to electron microscopes of the scanned transmission type, as well as to those of the non-scanned type.

Although the invention has been shown in connection with a preferred embodiment, it will be readily apparent to those skilled in the art that various changes in the form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. In an electron microscope comprising a source of electrons for producing a beam of electrons directed generally along an electron optical axis, and a specimen stage for supporting and controlling the position of a specimen in said beam, the specimen stage comprising:

a support;

first gimbal means pivotally carried by said support for rotation about a first axis; second gimbal means pivotally carried by said first gimbal means for rotation about a second axis which is inclined to and intersects said first axis;

specimen mounting means carried by said second gimbal means;

means for translating said second gimbal means relative to said first gimbal means in a direction parallel to said second gimbal axis; and

means for translating said specimen mounting means relative to said second gimbal means in a direction inclined to said second gimbal axis.

2. A specimen stage according to claim 1 wherein said first gimbal means comprises a tubular member.

3. A specimen stage according to claim 2 wherein said tubular member is removable from the remainder of the specimen stage.

4. A specimen stage according to claim 2 wherein said first axis is the axis of symmetry of said tubular member.

5. A specimen stage according to claim 2 wherein said second gimbal means comprises an annular member mounted within said tubular member.

6. A specimen stage according to claim 1 wherein said second gimbal means is pivotally mounted on said first gimbal means by means of journals which are supported in bearings, said journals being axially slidable within said bearings so as to allow translation of the second gimbal means relative to the first gimbal means.

7. A specimen stage according to claim 1 wherein said means for translating the specimen mounting means relative to said second gimbal means includes a push rod slidable along said second axis, and means for converting movement of said push rod into movement in said direction inclined to said second axis.

8. A specimen stage according to claim 1 wherein said support is mounted in the electron microscope so as to be movable in a plane transverse to the electron optical axis, whereby the point of intersection of said axes may be aligned with the optical axis.

9. An electron microscope including a specimen stage as claimed in claim 1. 

1. In an electron microscope comprising a source of electrons for producing a beam of electrons directed generally along an electron optical axis, and a specimen stage for supporting and controlling the position of a specimen in said beam, the specimen stage comprising: a support; first gimbal means pivotally carried by said support for rotation about a first axis; second gimbal means pivotally carried by said first gimbal means for rotation about a second axis which is inclined to and intersects said first axis; specimen mounting means carried by said second gimbal means; means for translating said second gimbal means relative to said first gimbal means in a direction parallel to said second gimbal axis; and means for translating said specimen mounting means relative to said second gimbal means in a direction inclined to said second gimbal axis.
 2. A specimen stage according to claim 1 wherein said first gimbal means comprises a tubular member.
 3. A specimen stage according to claim 2 wherein said tubular member is removable from the remainder of the specimen stage.
 4. A specimen stage according to claim 2 wherein said first axis is the axis of symmetry of said tubular member.
 5. A specimen stage according to claim 2 wherein said second gimbal means comprises an annular member mounted within said tubular member.
 6. A specimen stage according to claim 1 wherein said second gimbal means is pivotally mounted on said first gimbal means by means of journals which are supported in bearings, said journals being axially slidable within said bearings so as to allow translation of the second gimbal means relative to the first gimbal means.
 7. A specimen stage according to claim 1 wherein said means for translating the specimen mounting means relative to said second gimbal means includes a push rod slidable along said second axis, and means for converting movement of said push rod into movement in said direction inclined to said second axis.
 8. A specimen stage according to claim 1 wherein said support is mounted in the electron microscope so as to be movable in a plane transverse to the electron optical axis, whereby the point of intersection of said axes may be aligned with the optical axis.
 9. An electron microscope including a specimen stage as claimed in claim
 1. 